Double-sided pressure-sensitive adhesive tapes have been used widely for the adhesion between a molded or formed product and a member of household electric appliances and office automation equipment owing to its handling use and good adhesion characteristics. For example, there is known a releasable type double-sided pressure-sensitive adhesive tape including a nonwoven fabric as a support and pressure-sensitive adhesive layers disposed on both sides of the support, which is characterized in that it has a strength at yield point from 20 to 40 (N/20 mm) in each of the machine direction and transverse direction, an elongation at yield point not greater than 10%, and a strength at break higher than strength at yield point (refer to JP-A-2005-60633). There is also known a double-sided pressure-sensitive adhesive tape employing a nonwoven fabric made of Manila hemp (for example, refer to JP-A-9-272850, JP-A-2001-72951, JP-A-2000-265140, JP-A-2000-265143, JP-A-2000-303041, and JP-A-7-70527).
These double-sided pressure-sensitive adhesive tapes however have a problem that when the pressure-sensitive adhesive layers are formed on both sides of the nonwoven fabric by directly applying a pressure-sensitive adhesive thereto and drying, fine shrinkage wrinkles appear during winding and storing of the tape in the form of a roll after application and drying.
As a method of preventing such generation of wrinkles during storage, known is a manufacturing method of a double-sided pressure-sensitive adhesive tape comprising applying a solvent type pressure-sensitive adhesive to one side of a release paper subjected to release treatment and drying it to form a pressure-sensitive adhesive layer; attaching the resulting pressure-sensitive adhesive layer to both sides of a base material sheet, releasing one of the release papers, and then winding the base material sheet together with the other release paper; wherein after the solvent type pressure-sensitive adhesive is applied to the surface of the release papers prepared by directly applying a releasing agent to glassine paper, which surface has been subjected to release treatment, and the solvent pressure-sensitive adhesive is foamed at a foaming ratio of from 1.1 to 1.3 under heating, the resulting release papers are attached to the both surfaces of the base material sheet, respectively, one of the release papers is peeled and removed, and then the base material sheet is wound together with the remaining release paper (refer to JP-A-8-20754).
In the above-described method, however, the pressure-sensitive adhesive layer is formed by so-called transfer, that is, lamination after formation of the pressure-sensitive adhesive layer on the release paper. It is inferior in productivity to formation of the pressure-sensitive adhesive layer by direct application.
Moreover, in adhesion of small parts, when a half cut of a tape is performed with a release paper as a board or blanking processing is performed after the tape is attached to a foamed product, use of a stretchy tape sometimes results in reduction in a production yield because of deformation at the time of cutting or occurrence of defective blanking. A tape with smaller elongation is sometimes demanded. In such a case, an impregnant is ordinarily employed for decreasing the tape elongation and improving the tape tensile strength. However, a nonwoven fabric impregnated with an impregnant tends to cause shrinkage wrinkles when a pressure-sensitive adhesive is transferred to the fabric and thus adjustment of tension is necessary. Moreover, when a pressure-sensitive adhesive is applied directly, this problem cannot be overcome only by the adjustment of tension.
When a pressure-sensitive adhesive layer is formed by direct application, which provides good productivity, in particular in the case of a double-sided pressure-sensitive adhesive tape using as a support a nonwoven fabric containing an impregnant and exhibiting a small tape elongation, an effective means for preventing shrinkage wrinkles at the time of manufacture or storage has not yet been proposed.